High data rate signal transmission between integrated circuits requires a high degree of signal integrity. For example, at the gigabit data rate, a signal traveling over even a few centimeters on a conductor (“trace”) may experience sufficient delay and distortion to cause difficulty in recovery at the receiving end. Various methods for detection have been devised to increase detection sensitivity. Differential-pair signaling and single-ended pseudo-differential signaling are two methods that are often used.
In differential-pair signaling, two wires carrying complementary forms of a signal are provided for each physical channel. At the receiver, the transmitted signal is recovered by taking the difference of the signals on the two wires. As an external signal reference is not required at the receiver, differential-pair signaling uses “self-reference detection.”
In single-ended pseudo-differential signaling, only one wire is used to carry a data signal for each physical channel. The receiver compares the data signal with a reference signal. The signal reference may be self-generated or may be transferred from the transmitter.
While differential-pair signaling has better performance over single-ended pseudo-differential signaling, differential-pair signaling is typically less efficient, as it requires twice the wiring, and consumes twice the power. Single-ended signaling has a lower cost per channel, but single-ended pseudo-differential signaling typically has a lower performance because its lower signal sensitivity—i.e., the received signal has a larger uncertainty zone. Consequently, the received signal is more susceptible to a false detection due to noise, for example. This condition is referred to in the technical literature as having a “smaller eye-opening.”
To take advantage of its lower cost per channel, the prior art attempts to improve sensitivity and performance in the single-ended approach. One such signaling scheme is referred to as “JAZIO.” JAZIO compares a single-ended data signal with two phases of a clock signal transmitted with the data signal to achieve enhanced differential sensing at the receiver. JAZIO is described, for example, in (1) E. Haq, et al, “JAZIO Signal Switching Technology,” IEEE Micro, January-February 2001, pp. 72-81; (2) K. Krewell, “JAZIO Slow Edges Can Run Fast-A Novel Approach to High-Performance Bus Interfaces,” in Microprocessor Report, issue Feb. 21, 2000-2002, February 2000, pp. 1-4; (3) “Improving Performance of Parallel Interfaces using Steady State Voltage and Timing References”, JAZIO, Inc., JAZIO High Speed Digital I?O Signal Switching Technology white paper, Aug. 1, 2002.
Among the signaling techniques discussed above, the pseudo-differential signaling technique has the lowest receiver sensitivity. Differential-pair signaling technique runs at about one-half speed per trace, as two traces are used per data bit. In particular, in a wide parallel bus application, differential-pair signaling technique has poor bus signal integrity because of the complex signal coupling that results from switching signals carried on traces in close proximity. JAZIO signaling is complex in its generation of the signal references, and in its post-processing, which is required after the initial stage of detection.
Therefore, there exists a long-felt need for a high sensitivity signaling technique with a sensitivity performance comparable to differential-pair signaling without its high cost, and without the complex post-processing required in JAZIO signaling.